Int J Anat Res 2014, 2(3):459-61. ISSN 2321-4287 459
Case Report
NUM BERS M ATTER : CLINICAL SIGNIFICANCE OF ADDITIONAL
BELLY OF FIRST AND SECOND LUM BRICAL M USCLES OF THE HAND
Tintu TS *
1, Asha J M athew
2.
ABSTRACT
Address for Correspondence: Tint u TS, Lect urer, Depart ment of Anat omy, Amrita School of M edi-cine, Amrita Inst it ute of M edical Sciences, (Amrita Vishwa Vidyapeet ham) Ponekkara PO 682041, Kochi, India. E-M ail: t int ut s@aims.amrita.edu
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* 1 Lect urer, 2
Associate Professor.
Depart ment of Anat omy, Amrita School of M edicine, Amrita Inst it ute of M edical Sciences (Amrita Vishwa Vidyapeet ham), Ponekkara, Kochi, India.
In a rout ine dissect ion conduct ed in t he Depar t m ent of Anat om y, Am rita School of M edicine Kochi, addit ional origins of t he first and second lum br icals w ere observed on t he right hand of a m ale cadaver. The ad dit ional belly or iginat ed from t he radial side of t he t endon of flexor digit orum superf icialis (FDS) of t he index finger, deep t o t he flexor ret inaculum . Dist ally t he t endon of bot h bellies unit ed and insert ed t o t he dorsal digital expansion of t he index finger. In t he case of t he second lum brical t he addit ional belly arose from t he ulnar side of t he t endon of Flexor digit or um profundus (FDP) of t he index finger and inser t ed int o t he dorsal digital expansion of m iddle finger. Know ledge of possi ble variat ions helps t he clinician find aet iology for various com pressive syndrom es so t hat t reat m ent m odalit y can be t ailored and cust om ised. This presentat ion w ill add t o t he com pendium of infor m at ion.
KEYW ORDS:Addit ional belly, Flexor digit or um superficialis, Flexor digit orum prof undus, M edian nerve, Car pal t unnel syndrom e.
INTRODUCTION
Int ernat ional Journal of Anatomy and Research, Int J Anat Res 2014, Vol 2(3):459-61. ISSN 2321- 4287
Received: 16 June 2014
Peer Review : 16 June 2014 Published (O):31 July 2014 Accepted: 14 July 2014 Published (P):30 Sep 2014 Internat ional Journal of Anat omy and Research
ISSN 2321-4287 w w w.ijmhr.org/ ijar.ht m
The human hand is prehensile. The reason is t he presence of numerous small int rinsic muscles in t his region. The lumbricals are a set of muscles of t his group responsible for fine and delicate t asks such as sew ing and upw ard st rokes of w rit ing. The lumbrical muscles of t he hand flex t he metacarpophalangeal joint s and extend t he interphalangeal joint s. They are unique in t hat t hey have no bony attachment - proximally t hey are attached t o t he tendons of FDP and distally t o t h e ext en sor exp an si o n an d t h ereb y connect ing t he flexors and extensors [1].
They are numbered from lateral t o medial side as 1-4. The first and second arise from t he radial side and palmar surfaces of tendons and of index
and middle fingers respect ively. The t hird is from t he adjacent side of tendons of middle and ring finger and t he fourt h from adjoining sides of tendons of ring and litt le finger. They insert int o t he corresponding extensor expansion in t he vicinit y of t he metacarpophalangeal joint . The first t w o are unipennat e and t he last t w o are bipennate [2]. The innervat ion of t he lumbricals follow s t he innervat ion of t he parent unit of t he FDP and hence t he first t w o lum br icals are innervated by t he median nerve and t he medial t w o by t he ulnar nerve [3].
CASE REPORT
edi-Int J Anat Res 2014, 2(3):459-61. ISSN 2321-4287 460
Tint u TS et al., NUM BERS M ATTER : CLINICAL SIGNIFICANCE OF ADDITIONAL BELLY OF FIRST AND SECOND LUM BRICAL M USCLES OF THE HAND.
cine, Kochi, addit ional origins of t he first and second lumbricals w ere observed on t he right hand of a male cadaver. The origin of t he first lum brical was seen as a fleshy belly from t he radial side of t endon of t he flexor digit orum p ro f u nd u s (FDP) o f t h e i n dex f i n ger. Th e addit ional belly was seen t o originate at a more proximal level than the profundus belly. It s origin was seen as a t hin tendon on t he radial side of t he tendon of flexor digit orum superficialis (FDS) o f t h e i n d ex f in ger, d eep t o t h e f l exo r ret inaculum. Distally t he tendon of bot h bellies u ni t ed an d i n ser t ed t o t h e d o rsal d i git al expansion of t he index finger (Figure 1).
The second lumbrical was seen on t he radial side of t he FDP tendon of t he middle finger w hile it s addit ional belly arose from t he ulnar side of t he tendon of FDP of t he index finger, t he addit ional belly being m ore proxim al and in t he carpal t unnel. The origins w ere bot h fleshy and t he tendons of bot h bellies merged and inserted int o t he dorsal digit al expansion of m iddle finger (Figure 2). The first and second lumbricals w ere innervat ed by t w igs of t he lat eral branch of median nerve (Figure 3).
Fig. 1: Origin and insert ion of first lum brical and it s addit ional belly.
Fig. 2: Or i gi n and i nser t io n of second lu m br ical and it s ad di-t ional belly.
Fig. 3: Tw igs f rom t he l at eral b r an ch o f t h e m ed i an n er ve supplying t he f irst and second l u m b r i cal s i n cl u d i n g t h ei r addit ional bellies.
DISCUSSION
aut-Int J Anat Res 2014, 2(3):459-61. ISSN 2321-4287 461
Tint u TS et al., NUM BERS M ATTER : CLINICAL SIGNIFICANCE OF ADDITIONAL BELLY OF FIRST AND SECOND LUM BRICAL M USCLES OF THE HAND.
hors [4, 5]. Incidence of addit ional belly is more t han reduct ion in number [6]. It has been noted t hat t he lum bricals m ay have an occasional origin in t he forearm or from a metacarpal or from t he superficial instead of t he deep flexor tendons as in t his case in t he first lumbrical and t hat t h e t h i r d an d f o ur t h l u m br i cal s m ay originate from a single tendon instead of t wo [7]. There have been instances of t he origin of t he first lumbrical from t he flexor pollicis longus [8]. Phylogenetically FDS in mammals is homologous w it h t he int rinsic musculat ure of t he palm, and t hat it shift s it s origin proximally in t he forearm [9]. This account s for the possible origin from the FDS.
CONCLUSION AND CLINCAL SIGNIFICANCE
Presence of an addit ional muscle belly for t he first and second lumbricals as seen in t he present case has immense clinical relevance as such an occurrence may compress t he median nerve in t he carpal t unnel due t o t he incursion of t he m uscle w it hin t he carpal dur ing t he f inger movement s or by hypert rophy of t he lumbricals [10].
The t reat m ent in such cases of Carpal t unnel syn d r om e w o u l d b e i n cisi o n o f f l exo r ret inaculum, release of t he origin of m uscle i nv ol v ed o r even r esect io n o f t h e m uscl e involved [ 11]. Hence t he clinician m ust be co nst ant l y aw are o f su ch p o ssi b i l i t ies, alt hough preoperative diagnosis may be difficult .
Conflicts of Interests: None
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